Digital printing technology, such as dye sublimation or ink jet, is rapidly replacing conventional silver halide (AgX) printing technology in the marketplace. Modern retail AgX photolabs, often referred to as a “digital minilab” or DML, use a digital exposure engine, one or more rolls of photographic paper and a chemical processing unit. Digital images are transferred to the photo paper using the exposure engine. Prints can be made in a variety of sizes depending upon the size of roll loaded in the minilab as well as the capabilities of the digital exposure unit. Exposed photographic paper is transferred to a chemical processing unit from which finished pictures emerge after approximately 5 minutes. Modern minilab systems enjoy benefits such as speed and inexpensive consumables, but are relatively expensive to purchase and use hazardous chemicals.
Digital printing technology, such as dye sublimation printers, have a smaller physical footprint, use no hazardous chemistry and are significantly less expensive than digital minilabs. Digital printing technology typically has a higher operating cost (consumables) which is offset by the lower purchase print and service fees. To achieve comparable printing speeds to digital minilabs, multiple printers can be used simultaneously. As an example, three dye sublimation printers that are each capable of printing 500 unique prints per hour can be combined to produce 1,500 prints per hour. In order to fully benefit from this speed potential, consumer print orders that usually consist of 27 or more prints per order must be spread across the number of printers that are available.
One challenge caused by using multiple printers is calibration. In general, digital printers are manufactured and factory calibrated to a set standard. However, some unit to unit variation does exist. This variation may grow as printing units age. Color management technology, such as ICC (International Color Consortium), is often used to calibrate each individual printer to a set standard. Printers can be calibrated (or profiled) as needed or on a periodic basis to ensure consistency. Printer profiles are created by printing specific color target sheets (i.e., printed sheets having a known pattern of colored patches), reading the target sheets using a spectrophotometer, and processing the results using specialized software to determine the variance of the printed colored patches on the target sheets from the intended target pattern, and to establish a printer calibration profile adjusting the print settings to match the intended target pattern. The number of colored patches that must be printed to create a calibration profile for each printer varies based upon the desired accuracy of the calibration profile and the size of the paper used to print the target sheets. As an example, 5-4×6 target sheets must be produced to create a calibration profile using 729 colored patches on the target sheets. An example of a target sheet formed of colored patches of typical configuration is shown in FIG. 1. While FIG. 1 depicts a target sheet having individual patches shown in varying shades of gray, those of ordinary skill in the art will recognize that in a typical target sheet, such individual patches are in fact color patches of varying colors to properly allow for color calibration across a wide spectrum of colors.
When using multiple printers, it is typically desirable to ensure that each printer prints images as nearly identical to one another as possible. For instance, because many photo customers desire multiple photo prints in their order, it is important to ensure that an order that has been routed to multiple printers for faster processing is printed such that the same image printed on two different printers looks identical in each print. Regular calibration of the printers is important to ensure that such separate printers maintain the ability to print the same image in as much of identical form as possible. Photo print labs will thus typically have a policy governing frequency of printer calibration. To perform such calibration, a computer at the lab typically runs an application which lets the lab operator print target sheets from specifically selected printers. Those target sheets typically include human readable text and/or labels on each page indicating, for instance, “Sheet X of Y” (i.e., the number X of the current sheet in a collection of Y target sheets for the specific printer undergoing calibration). Once those sheets are printed, the application typically allows the operator to perform a calibration function for a specifically selected printer, in which case the application instructs the user to scan specific target sheets for that selected printer using a spectrophotometer. The user must closely follow the instructions, feeding the specifically instructed sheet into the spectrophotometer at the designated time, in order for the software to generate the appropriate printing profile for the designated printer. After the required target sheets for the designated printer are fed through the spectrophotometer, the software gives the user various options to configure the print profile, and to associate that profile with one or more individual printers.
Because it is becoming common for multiple printers of the same size to be used in digital photo labs, a lab operator may thus need to handle between 15 and 20 printed pages when re-calibrating a system. These pages must be kept and processed in the correct order to build calibration profiles. While the process of calibrating a single printer may be complicated and time consuming, the process of calibrating multiple printers thus adds a level of complexity for the lab operator, requiring them to manage and maintain in proper order multiple target sheets from multiple printers to ensure that each target sheet being processed is recognized as having been generated by the specific printer for which a profile is to be generated. A method to simplify this calibration process is thus highly desirable.